

A056723


Numbers k such that 8*10^k + 3*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.


1



1, 7, 23, 29, 133, 173, 367, 1925, 3707, 5765, 9709, 19573, 43753
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OFFSET

1,2


COMMENTS

Also numbers k such that (25*10^k  1)/3 is prime.


LINKS



MATHEMATICA

Do[ If[ PrimeQ[ 8*10^n + 3*(10^n1)/9], Print[n]], {n, 0, 10000}]


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS

Corrected by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
19573 and 43753 from Serge Batalov, Jan 2009 confirmed as next terms by Ray Chandler, Feb 13 2012


STATUS

approved



